1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems for deploying geophones for collecting and seismic data and, more particularly, to mechanisms and techniques for mechanically deploying the geophones.
2. Discussion of the Background
Land seismic data acquisition and processing may be used to generate a profile (image) of the geophysical structure under the ground (subsurface). While this profile does not provide an accurate location for oil and gas reservoirs, it suggests, to those trained in the field, the presence or absence of such reservoirs. Thus, providing a high-resolution image of the subsurface is important, for example, to those who need to determine where oil and gas reservoirs are located.
Traditionally, a land seismic survey is performed in the following way. Plural geophones electrically connected to each other need to be deployed on the ground or below the ground. This process is very labor-intensive because thousands of geophones need to be deployed. Seismic personnel mark the desired locations of the geophones and manually dig a hole for each geophone. After the geophone is manually deployed into its corresponding hole, the seismic personnel manually cover the geophone with the dug dirt.
As this process may last for hours if not days, the seismic personnel become tired and may not compact the dirt on top of the geophone. Also, the bottom of the hole may not match the shape of the geophone. Thus, pockets of air may be left between the geophone and the dirt around it. These pockets will modify the velocity of the ground recorded by the geophone, i.e., will deteriorate the recorded signals.
After all the geophones have been deployed, one or more seismic sources are brought into the field and actuated to generate the seismic waves. The seismic waves propagate through the ground until they are reflected by various reflectors. The reflected waves propagate to the geophones, where a movement of the earth is recorded. However, if the coupling between the geophone and the dirt around it is not good, the recorded data is poor.
The conventional geophones 100 are either placed on the ground 102 as shown in FIG. 1, or buried, manually, in a small hole 204 in the ground and then covered with dirt 206 for a better coupling. A geophone typically has a cylindrical shape and a small size, e.g., around 3 cm long and 2 cm in diameter. Thus, coupling between the geophone and the ground might be a problem. The coupling may be achieved by the weight of the geophone or by other means, e.g., a spike connected to the geophone and inserted into the ground. However, the coupling between the ground and geophone is not well understood. The geophone-ground coupling may be defined as the difference between the velocity measured by the geophone and the velocity of the ground without the geophone. This definition is appropriate for designing a geophone.
However, once the geophone is designed and needs to be deployed, the practicing geophysicist has to deal with the fact that the geophone may not be appropriately deployed. For example, the geophone may not be coupled “well” to its surroundings. In this situation, the above definition might not be appropriate. For this situation, those skilled in the art would consider that a bad geophone coupling refers to the difference between the velocity as measured by the badly planted geophone and the velocity as measured by the well-planted geophone.
Irrespective of the definition to be used, the ground-geophone coupling is a persistent problem in the field. Weight coupling generally is not well-behaved because the contact area between the geophone (or another sensor) and the ground is rough. Often, the only way to improve the coupling is to increase the mass of the geophone so that the contact with the ground becomes better (stronger coupling resulting in more regular contact area). In practice, geophones are kept lightweight because of weight limits imposed on transporting thousands of geophones. Thus, the requirements for (1) light weight and (2) a good coupling by weight work against each other.
Therefore, there is a need to improve the coupling of the geophone to the ground without increasing the weight of the geophone to improve the quality of recorded data.